Method of recovering compounds from zinc and lead ores



Jan. 26, 1937. T. A. MITCHELL 2,068,690

METHOD OF RECOVERING COMPOUNDS FROM ZINC AND LEAD ORES Filed Jan. lO, 1955 [Hear SoLur/on/ 'ro 64%] Pue/F105 -r/ u N Recm/ rn rlofv ,qr 64 Evapoeqre @No NQCI Ho CRYSTHLLIZE our H20 Tifo/VHS H. MITCHELL j QQOQR Patented Jan. 26, 19317l STATES PATENT OFFICE METHOD F RECOVERING COMPOUNDS FROM ZINC AND LEAD ORES Thomas A. Mitchell, Inglewood, Calif., assigner to Hughes-Mitchell Processes, Incorporated, Deliver,n Colo., a corporation of Wyoming Application `llanuary 10, 1935, Serial No. 1,186

9 Claims. (Cl. 'J5-120) This invention relates to the recovery of lead fate. Thisaccomplishes many useful results. In and zinc compoundsfrom a complex ore mateparticular, the use of zinc sulfate instead of some rial, and particularly to the production of lead other reagent serves to introduce no 'ion into sulfate and various compounds of zinc. the solution which cannot be readily removed Lead is commonly found associated with zinc from the brine and usefully employed in the 5' and other `ore metals in sulfide ores, and many process. ItA is. especially advantageous that the problems have been met heretofore in thesepareagent is 'a principal ingredient of a common ration of these ore metals and their direct relead ore, so that one element of the ore may be covery as valuable compounds. In fact, many used in the recovery of another. Hence, by re- 10 processes, such as ore smelting, ywhich serve for moving the zinc from the complex sulde ore 10,

recovering either of these metals from a simple as a sulfate, this product may be returned to -l ore, do not recover both of the metals when the process and employed usefully to take all of the two eiciently or economically are found intiresidual lead chloride from solution. That is,

mately associated in acomplex ore. zinc sulfate reacts with the complex brine conl t l5 One object of the .invention is to so treat such taining lead, sodium and chlorine ions and're- 15.

a complex lead and zinc ore that lead and zinc moves all of the lead therefrom as insoluble lead compounds may be recovered serially, and parsulfate. Also, zinc sulfate will precipitate lead ticularly to provide a method in which the zinc sulfate from Water solutions of lead chloride, ni-

of the ore may aid in the production of the detrate or acetate derived from any suitable sources.

2o sired lead compound. By using this reagent, it is possible by the pro- 20 A further object comprises so carrying on `the cedure .herein described both to make the detreatmentof a complex lead and zinc ore masired leadsulfate and to obtain a valuable zinc terial that the lead and zinc may be recovered compound; hence, both reagents are converted by a low temperature solution and precipitation to useful materials, and if'desired the process may method which, in particular, results in the `probe partly cyclic in nature. 25

- duction of valuable lead and zinc compounds In thepreferred practice of the invention, a

without necessitating converting the lead and 'complex ore containing lead and zinc compounds zinc of the ore material to metals as intermediate 1 may beso treated as to recover a solution of zinc products. 'f sulfate therefrom and to leave the lead in solu- In accordance with onephase of this process, tion in a hot sodium chloride brine, whether the 30 t lead may be recovered from such a complex ore lead was originally in the `form of lead sulfate or from other desired materials as a solution of or lead chloride. Bycombining the zinc sulfate, lead sulfate and/or chloride in a hot sodium either in solution or as a dry salt, and the lead chloride brine or as a water solution'of lead salt brine in proper proportions and under suitnitrate, chloride or acetate. A` further object able conditions, leadsulfate may be directly pre- 35 of this invention is, therefore, to so treat such cipitated froni this brine and the zinc will then a solution that lead sulfate may be produced remain in solution `as zinc chloride. This resulttherefrom by a: method which is efficient and ant solution may thereafter be so treated 'as to economical and whichvdoes not add tothe solurecover the zinc therefrom and, if desired, the 40 tion any ions incapable of being easily recovchlorine ion may be again cyclically used inthe 40 ered or which are detrimental to subsequent steps process. of the process. Further objects will be apparentv The precipitation of lead sulfate from a. salt in the following-disclosure.. brine by means of zinc sulfate applies to the 'I'he drawing illustrates as a flow dlag'ramthe treatment of such a brine solution, from whattreatment of a complex ore material which reever source it may be derived; but in' order that 45 sults in the recovery of lead sulfate 4and zincthe entire process may be illustrated and decarbonate, hydroxide or oxide, but the drawing scribed, reference is to be had to the accompanyis merely illustrative of one phase of the inven. ing drawing, which shows how a complex ore mation SIICBOther lead bearing materials may be terial containing lead and zinc suldes may .be

5 treated for the production of lead sulfate thereso treated as to recover both the lead and the 50 from. zinc as valuable marketable substances.

In accordance with this invention, lead sul- An ore containing lead and zinc sulfides may fate may be precipitated froma sodium or other be preliminarily treated, as by a roasting operalkali metal chloride brinesolution of .lead chloation, to convert a considerable portion of the 55 ride and/or lead sulfate by means of zinc sulzinc sulfide to zinc oxide and/or zinc sulfate, and

the lead sulfide is preferably converted to the sulfate. Then, by leaching the roasted ore material with a dilute sulfuric acid solution, a solution of zinc sulfate is thereby recovered. This procedure may be carried on in accordance with standard practice and under suitable conditions to give a solution of required concentration, such as by repeatedly leaching the ore material with the same solution until it has been suiciently concentrated for the reaction hereinafter described. If iron is present in the ore, a considerable amount of zinc oxide is left in the roast so as to prevent iron from going into the zinc sulfate solution, but all of the water soluble zinc compounds are to be removed, as by a second leaching operation, before the lead sulfate is dissolved. The recovery of the residual zinc in the ore is not a part of this' invention, but it is to be understood that the zinc may be solubilized and recovered by any suitable procedure, such as that set forth in' the prior Mitchell Patents Nos.

1,979,281 and 1,943,340, in accordance with which sodium or potassium chloride so as to dissolve theA lead sulfate therein. If the ore has been treated in accordance with the Mitchell process to form zinc chloride from the residual zinc compounds, as set forth in the Mitchell patents, then the 'nisher product is preferably leached with-water to remove all ofthe soluble Zinc and other compounds which might contaminate the salt brine solution. Thereafter, the zinc-free ore material is treated with the hot neutral salt brine to dissolve the lead sulfate and/or chloride in the nisher residue. The brine is preferably a concentrated solution of sodium chloride which is held at a temperature of C. during the step of dissolving the lead sulfate and chloride, and the resultant solution may be saturated `with respect to the lead.

The brine used for leaching the lead from the ore material may contain a considerable proportion of sulfate ions derived from thelead sulfate and be cyclically used in the process; but as sodium sulfate accumulates in the system, it should be separated from this brine by a suitable procedure, such as b'y evaporation and crystallization, whereby. the crystals of sodium suifate will be removed from the NaCl solution. This avoids having too -strong a concentration of sulfate ions in the brine and thus impeding the solubilizing of the lead from the ore material. The lead bearing brine solution may contain other undesired compounds, in accordance with the nature of the ore material which is being treated, and these compounds Will be suitably removed from the hot salt brine by any standard procedure which does not add objectionable ions to the so- .lution, so that the salt brine will be of such a composition that only lead sulfate will be precipitated during the stage of treatment with the zinc sulfate. plied to the lead salt brine since the undesired elements may be more easily removed4 at this This purification is preferably ap` aoeaeeo stage than after the precipitation of the lead sulfate. For example, iron in solution may be removed by precipitating it as ferrieI hydroxide. For this purpose, one may use standard reagents for oxidizing the ferrous iron to the higher form and then converting it to the hydroxide. After the iron and other impurities have been precipitated, they are removed from the brine, as by ltration.

This brine is preferably raised to and held at a temperature of 84 C. so that it will not be saturated with respect to the lead and sodium ions therein during the purification and the sub-i sequent step of precipitating the lead sulfate. Consequently, lead and sodium chlorides will not be precipitated by a minor temperature change. While maintained at this temperature of 84 C., the lead-sodium chloride brine, which may contain sodium sulfate, is'combined with the zinc sulfate solution of substantially the same temperature, although dry zinc sulfate may be used if desired. 'Ihe concentrations of the two solutions are preferably high and so chosen that the process will be efficient and economical; but because of this high concentration, care has to be taken to insure that undesired compounds do not appear in the lead sulfate. It is, therefore, desirable to satisfy the temperature requirements above voutlined and to employ that concentration of zinc sulfate solution which, according to stoichiometric calculations, Will serve to precipitate the lead. It is to be appreciated that in the above discussed reaction, we are dealing with the chemistry, not of a water solution, but of a sodium chloride solution of the lead compound containing sodium, lead and chlorine ions. When the hot solution is cooled, what is believed to be a compound of the formula :rPbClz.yNaCl crystallizes out, hence the avoidance of the formation of su'ch a precipitate is necessary.

The lead sulfate thus precipitated may be removed from the solution by any suitable filtering apparatus or equivalent procedure and dried and subsequently treated as desired for use in the industries. other treatments employed to insure a suitable purification thereof.

uThe solution resulting from this precipitation treatment contains zinc, sodium, chlorine and sulfate ions. In order to recover the zinc therefrom, the solution may be treated with dry sodium carbonate or with any suitable solution containing sodium and the carbonate whether or not kother elements or ions, such as hydroxyl, sulfate and chlorine, are present, proi vided the precipitated product is the desired zinc' carbonate. The term sodium carbonate as herein used is, therefore, intended to cover all such equivalent reagents, whether derived from natural or artificial sources and whether used as dry salts or as solutions thereof and Without regard to harmless impurities or re-y It willy be washed with water andi ions, v

agents associated therewith. If hydroxyl ions v tions in composition depending on the tempera-v ture of precipitation, etc. One may also precipitate the zinc as the hydroxide by means of sodium hydroxide. This serves likewise to leave sodium, chlorine and sulfate ions in solution; hence the remainder of the process may be carried on as herein described. Neither the carbonate nor the hydroxide of sodium leaves new and undesired ions in the solution. The various precipitating steps will be carried on under suitable conditions of temperature, rate of adding the reagents, agitation of the solution, etc., as are desirable. The result of treating this zinc bearing solution with the carbonate salt leaves the zinc wholly as a precipitate, and the proportions of the ingredients Will be in such amounts as are found by analysis to accomplish the precipitation of fall'of the zinc from the solution. Then, by ltering o the precipitate and washing it, the zinc compound isrecovered. 1f desired, the zinc compound, whetherra carbonate or an hydroxide, may then be calcined under required conditions to convert it vto zinc oxide, which is of large use in the industry.

The resultant solution containing sodium, chlorine and sulfate ions is now ready for return to the step or' leaching the ore material to remove the lead therefrom. As above suggested, this brine may be heated suiciently to evaporate water therefrom and cause the crystallization of that excess of the sodium sulfate which is not desired in the brine. Then, the purified brine is returned for solubilizing more of the lead sulfate and/or chloride in the ore material, after its concentration and temperature have been adjusted.

Instead of a brine solution of lead, one may employ soluble lead compounds in water solution, such as lead chloride, nitrate or acetate.

`The aqueous solution of lead chloride is to be heated, as above described, to hold the lead in a solution which is not quite saturated. Lead nitrate and acetate will also serve for reacting with zinc sulfate with a resultant formation of lead sulfate and Zinc nitrate or acetate in solution. The zinc in solution, after separation from the lead precipitate, may be in turn thrown down by the strong sodium carbonate solution, thus leaving sodium nitrate or acetate in solution.

Any suitable reagent capable of lproviding car-A n brine and treating the hot solution with the zinc sulfate to precipitate lead sulfate therefrom, and thereafter recovering the lead sulfate.

2. The method of treating a lead and zinc sulfide ore comprising the steps of roasting the ore under oxidizing conditions and. forming oxygen compounds of the lead and zinc, dissolving zinc from the ore as zinc sulfate, recovering the lead from the ore residue as a hot sodium chloride solution of lead sulfate and/or chloride, thereafter treating the hot brine with the zinc sulfate and forming a-precipitate of lead sulfate and a brine containing zinc chloride, recovering the lead sulfate and treating the brine with a ree agent capable of furnishing carbonate and/or hydroxyl ions and precipitating the zinc for re-l covery therefrom.

3. The method of claim 2 in which the yzinc is precipitated by sodium carbonate and/or hydroxide and the resultant solution containing soldium chloride is available for dissolving more lead.

4. The method of recovering lead from an ore material containing lead sulfate and/or chloride comprising the steps of solubilizing the lead compound and separating it from the ore material as a hot brine solution containing lead, sodium and chlorine ions, treating the brine, while heated to a temperature at which the lead remains in solution, with zinc sulfate in stoichiometric proportions and forming a precipitate'of lead sulfate, and thereafter separating the precipitate from. the brine solution and recovering the lead sulfate.

5. The method of treating an ore material containing lead chloride and/or sulfate comprising the steps of dissolving the lead in a strong sodium chloride brine at about 75 C., thereafter heating the brine to a temperature at which it is not saturated with respect to the lead and sodium ions and treating the heated brine with zinc sulfate and precipitating lead sulfate therefrom, and recovering the lead sulfate.

6. The method according to claim 5 in which the nal solution is treated with sodium car- I bonate and/or hydroxide and the resultant precipitate is thereafter .removed from the solution and caloined to form zinc oxide.

7. The method of treating a complex lead and zinc sulfide ore comprising the steps of roasting the ore to provide oxygen compounds of lead and zinc, dissolving the zinc compound as a sulfate, recovering the lead as a hot sodium chloride solution or lead sulfate and/or chloride, treating the brine solution with zinc sulfate proportioned to precipitate lead sulfate therefrom, removing the lead sulfate, thereafter treating the residual solution with a reagent capable of furnishing carbonate and/or hydroxyl ions and precipitating the zinc for removal from the solution, whereby both lead and zinc are recovered serially from the ore.

8. The method according to claim 7 in which lead sulfate is initially dissolved in a hot sodium chloride brine and the last stage brine which is k free from lead and zinc compounds is heated to evaporate the water and crystallize sodium sulfate therefrom and the sodium chloride brine is then returned for dissolving vmore lead sulfate THOMAS A. MITCHELL. 

